Percutaneous vertebroplasty is a minimally invasive interventional radiological procedure that consists on injecting bone cement (Polymethylmethacrylate, PMMA) in the vertebral body, by trans-pedicular or oblique approach through a bone biopsy needle.
It was developed in France in 1984 for the treatment of aggressive or painful haemangiomas of vertebral bodies. For its analgesic effect, its use was quickly extended for the treatment of lytic metastatic lesions or myeloma and mainly in fractures or vertebral collapse due to osteoporosis. The procedure is indicated in those cases that are presented with severe and disabling pain that doesn't respond to conservative measures such as: corset use, analgesic and anti-inflammatory treatment or bed rest.
Most of the patients with this suffering are between the 6th and 8th decade of life. In this group of advanced age, the immobilization resulting from vertebral fractures has severe consequences in their general medical conditions, it predisposes them to cardiopulmonary, intestinal, circulatory complications, etc. Besides pain, the psychological effects can be devastating, it deteriorates the quality and reduces the expectation of life.
Vertebroplasty is a procedure that is carried out in hospital facilities that requires specialized medical personnel. It is performed in a hemodinamia room or cath lab, and it requires of the use of radiological equipment with high resolution fluoroscopy, mounted in a C arm. Currently, this injection is carried out in a manual and direct way and the operator is exposed to ionizing radiation every time that he/she practices a vertebroplasty. The injection of bone cement is made with fluoroscopic control, connecting an insulin syringe to the needle. This implies that the surgeon is in direct contact with the patient and therefore, overexposed to primary or secondary ionizing radiation during the lapse of the procedure of the vertebroplasty.
The primary radiation is the X ray beam coming from the X ray tube and received by the patient in a direct way, The secondary radiation it the one resulting on the deviation of the primary beam in the patient's body tissues and doesn't contribute to the formation of a diagnostic image, it is spread in all directions and it is the main source of exposure of medical personnel.
The insulin syringe is used since a small diameter barrel is required to have less resistance for the manual injection of high viscosity bone cement, each syringe is filled approximately in half or two thirds of its capacity to avoid bending or breaking the plunger when exercising the required injecting pressure that may be considerable. The volume needed to obtain the expected results varies from 3 ml up to 9 ml, therefore, 5 to 18 syringe exchanges are necessary, this favors the solidification of the polymethylmethacrylate and it can prevent to inject the wanted quantity.
If larger diameter syringes are used, the manual pressure is insufficient due to the density and viscosity of the bone cement; and becomes necessary the employment of a mechanical device to be able to exercise the required pressure. At the state of the art, there are commercially available devices such as pressure gun type or threaded plunger mechanisms connected directly to the needle that deposits the cement in the bone or through a high pressure short tube. The use of a long tube would have considerable resistance to the flow of the cement, favoring its solidification.
In most of these devices the syringe is not interchangeable, it is loaded with the total volume to inject and therefore, are of larger diameter and the increased resistance to the flow of the cement becomes worse with time due to solidification of cement.
On the other hand, the conventional hypodermic syringes are not designed for high pressure injection, the plunger and the fingers supporting wings bend easily.
The devices of the previous technique solve only the mechanical problem of injecting the dense and viscous cement through the needle but they are focused on exercising the necessary pressure directly on the patient or at a very short distance of the radiation source. They don't allow the operator to maintain an appropriate distance to reduced exposure to secondary radiation at acceptable levels according with the international radiological protection norms.
On the other hand, some mechanical devices do not allow control or manual sensibility of the exercised pressure and speed of the injection of the cement, important factors in the prevention of undesirable leaks and complications. Some devices that apply cement in the current state of the art are for example:
The patent application of the United States of America No. 2003/0018339, for Higueras et al, published Jan. 23, 2003, it discloses an application device for the controlled injection of hone cement, mounted in a syringe loaded with the cement, as a cartridge, which is discharged by a threaded metallic plunger placed in the other end of the device, it is useful for controlling the pressure exercised on the plunger of the syringe but it is a short device in which the operator is near the patient; It also contains the total load of cement.
On the other hand, due to the viscosity of the cement and quantity keeps certain dynamic memory that doesn't allow sudden interruption of the injection.
The patent application of the United States of America No. 2002/0156483, for Voellmicke et al, published Oct. 24, 2002, discloses a vertebroplasty device and bone cement, it contains two compartments, one for mixture of the cement and the other for storage and injection into the bone. This dual camera device for blending and injection, consists of a lodging camera with a plunger moving in an axial way, the cameras are in communication by a check valve that only allows the passage of the cement in one direction. An extra force can be exercise on the plunger by means of a lever that increases the mechanical force and therefore the pressure in the injection camera. This is a device in which it is necessary to work the piston of the blending camera and the piston of the injection camera to empty one and fill the other one alternatively. It is a short device, it is necessary to be near the patient and doesn't reduce the exposure to secondary ionizing radiation.
The patent application of the United States of America No. 2002/0099384, for Scribner et al, published Jul. 25, 2002, discloses a system and method to treat vertebral bodies. It is a special syringe with two concentric plungers. The first camera that has a first transverse section and a second smaller camera than the first one. Both cameras communicate to each other. The first camera includes a gate to receive the material inside the filling instrument, the second camera includes a gate to discharge the contained material. A first plunger suited to pass through the first camera and displace the material. A second plunger to pass through the interior of the first plunger's concentric hole and reach the interior of the second camera to displace the material through the exit in the second camera to inject into the needle toward the interior of the vertebral body. Although this device provides control in the injection of the bone cement, the operator is too near the patient.
In general the injection devices have a bolster that impels the viscous fluid by means of a manual trigger moved by a screw mechanism (inclined plane), there are others that have a gun like body such as the device of the Patent Application of the United States of America. 2002/0049448. for Sand et al, published Apr. 25, 2002, It has a tubular body that stores a viscous flowing material (bone cement), it is a longitudinal body with a providing end and a driving end, a plunger housed inside the tubular body that displaces the flowing material along the longitudinal axis of the tubular body, the driving mechanism has a handle like a gun to hold with a hand, while injecting with the other hand by means of the plunger that advances due the pressure exerted by a threaded mechanism. These mechanisms with big deposits have the inconvenience that the cement can end up solidifying in the conduit at the time of application and impede to apply the total amount of cement inside the affected vertebral body. On the other hand, with the excess of pressure generated by these devices, the cement could leak outside of the vertebral body, since the fluid (PMMA), for its viscosity, possesses a remaining flowing memory that may be difficult to control.
The Patent of the U.S. Pat. No. 6,348,055, for Preissman, published Feb. 19, 2002, protects a bone cement applying device with screw mechanism in which the preparation of the total volume of cement is made, this mechanism has an intermediate stabilizer that avoids the turns of the whole device during the application of pressure to the fluid. The stabilizer is a lever perpendicular to the screw body that can be sustain with a hand, while with the other hand exercises the pressure to inject the cement inside the vertebral body. This device is also operated very near the patient and therefore, the operator is exposed to secondary ionizing radiation. Another inconvenience is that if the cement solidifies in the system and has not reached the vertebral body in the proper amount, it is necessary to make another preparation previous placement of another needle in a different and appropriate position for the new requirement.
The Patent Application of the United States of America No. 2002/0010431, for Dixon et al, published Jan. 24, 2002, discloses a screw device for high pressure with a threaded axis that impels a plunger inside a camera full with viscous bone cement. This device has the inconvenience that one doesn't have manual sensitivity and control of the pressure exercised, it is not easy to exchange the syringes with the bone cement. As a matter of fact, it is the only syringe of the cartridge.